THERESA May’s official spokesperson has rejected claims from the former head of the diplomatic service that Cabinet infighting has hindered official Brexit talks.

Sir Simon Fraser, who led the Foreign Office staff until 2015, told the BBC the government has so far been “a bit absent” from negotiations in Brussels due to divisions on key policy areas, claiming the discussions “have not begun well”.

The comments come after the Prime Minister publicly contradicted Chancellor Philip Hammond on attempts to secure a transitional agreement on trade.

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But yesterday Downing Street said it would “disagree strongly” with the assertions, stating: “The last two months, we have had a constructive start to the negotiations. We have covered a significant amount of important ground.

“As the Secretary of State for Exiting the European Union said at the end of the last negotiating round, important progress has been made in understanding one another’s positions on key issues.”

Fraser, who advises businesses on Brexit and foreign policy, said: “The negotiations have only just begun, I don’t think they have begun particularly promisingly, frankly, on the British side.

“We haven’t put forward a lot because, as we know, there are differences within the Cabinet about the sort of Brexit that we are heading for and until those differences are further resolved I think it’s very difficult for us to have a clear position.”

Further “position papers” on customs arrangements and the Northern Irish border are due in the coming weeks and Fraser said this would show the UK is “ready to engage”.

He said: “So far we haven’t put much on the table apart from something on the status of nationals, so we are a bit absent from the formal negotiation.”

Downing Street also played down weekend press reports that the government is ready to pay a £36 billion “divorce bill” to the EU in order to secure a free trade deal with the bloc after Brexit, following an angry response from some Tory MPs.

The Prime Minister’s spokesman said although the UK accepted there would have to be a “fair settlement” in respect of the UK’s outstanding liabilities, the figure was not known.

He said: “The Prime Minister made clear in the letter triggering Article 50 that the UK and the EU need to discuss a fair settlement of both our rights and our obligations as an EU member state, but in terms of this figure I don’t recognise it.”

Meanwhile, EU budget commissioner Guenther Oettinger warned UK payments will have to continue following Brexit in March 2019 as Britain will remain “bound” by previous commitments.

He told Germany’s Bild newspaper: “London will therefore have to transfer funds to Brussels at least until 2020.”

Downing Street said ministers had already accepted that there would be obligations which would “survive” the UK’s withdrawal and that these would have to be resolved.

The UK made a net contribution to the European Union of roughly £156 million a week in 2016-17, the lowest level for five years.

Figures published by the Treasury suggest the total amount for the 12 months to March 2017 was £8.1 billion. It is the first time a figure has been estimated for the period that included the referendum.